Research Summary Human cytomegalovirus (CMV) is a ?-herpesvirus that can cause morbidity and mortality in immuno- compromised individuals including newborns and transplant patients. In newborns, CMV-associated neurological disorders represent the leading cause of birth defects affecting infants worldwide. Additionally, CMV causes gastrointestinal disorders, pneumonia, CMV syndrome, and end-organ disease in transplant recipients and is linked to early vascular damage resulting from infection of endothelial cells and macrophages. The anti-viral drugs ganciclovir and fomivirsen have limitations including poor oral bioavailability, dose-related toxicity selection of drug resistant viral mutants and are precluded for use in pregnant women. An alternative therapy is human cytomegalovirus immune globulin (CMV-IGIV, Cytogam) derived from human plasma with high titer CMV antibodies. Yet, there are significant drawbacks to its use as an effective therapeutic including the large treatment dose (100-150mg/kg) that drastically raises the risk of renal failure, limited efficacy in pregnant women and transplant recipients, and the possible transfer of human pathogens to the patients. Despite the short-comings of CMV-IGIV, the specificity, safety profile, and pharmacological activity of immunoglobulin-based therapy provide the rationale for the development of effective anti-CMV biologics. Given that CMV has the ability to infect multiple cell types such as fibroblasts and epithelial, endothelial, and myeloid cells, effective cross-reactive neutralizing monoclonal antibodies (mAbs) need to target conserved envelope proteins in all viral strains utilized to infect all cell types. Thus, we hypothesize that using multiple CMV strains as immunogens will generate broadly neutralizing mAbs to numerous envelope proteins that participate in virus infection and dissemination. We will test our hypothesis by completing the following Aims: 1) Functional screening of neutralizing mAbs that inhibit virus infection and 2) Identification and characterization of broadly neutralizing mAbs to diverse envelope proteins. From these studies, we expect to identify the viral envelope proteins that participate in virus infection of diverse cell types and the key envelope proteins that should be targeted to prevent virus infection and dissemination. Additionally, the VelocImmune animals used to generate the neutralizing mAbs would have an immediate impact for the development of anti-CMV therapeutics for patients at-risk for CMV-associated disorders.